Projector apparatus for preventing degradation in image quality due to heat

ABSTRACT

A projector apparatus includes a color separation optical system which separates illumination light into color light components, image forming panels illuminated with the color light components, respectively, a color synthesis optical system which synthesizes the light components from the illuminated image forming panels, and a projecting optical system which projects light from the color synthesis optical system. Transparent substrates are arranged on at least one of incident and exit surface side of the image forming panels. Each of the transparent substrates holds a polarizer. A surface area of at least one of the transparent substrates is larger than those of the remaining transparent substrates.

This is a continuation Ser. No. 10/629,113, filed Jul. 29, 2003 now U.S.Pat. No. 6,877,858, to which priority under 35 U.S.C. §120 is claimed.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a projector apparatus for displaying anenlarged computer image or video image.

2. Related Background Art

In recent years, image display apparatuses such as liquid crystalprojectors are required to improve brightness. FIG. 15 shows thearrangement of a conventional projecting image display apparatus(projector apparatus).

Referring to FIG. 15, white light emitted from a light source section101 of an ultrahigh-pressure mercury-vapor lamp is reflected by areflector 102 and transmitted through fly-eye lenses 103 and 104. Thedirection of polarization is aligned through a PS conversion element 105by a mirror which separates light into p-polarized light and s-polarizedlight and a λ/2-plate which changes the polarization direction. Thelight that emerges from the PS conversion element 105 passes through acondenser lens 106 and the like. After that, a red-band light componentis transmitted through a dichroic mirror DM101. Green- and blue-bandlight components are reflected by the dichroic mirror DM101. Theblue-band light component is transmitted through a dichroic mirrorDM102. The green-band light component is reflected by the dichroicmirror DM102. With this arrangement, the illumination light is separatedinto the light components in the red, green, and blue bands.

Each color light component becomes incident on a corresponding one ofliquid crystal display elements 109R, 109G, and 109B and is modulated.These color light components are synthesized by a dichroic prism 111 andenlarged and projected onto a projection surface by a projecting lens112.

Each color band will be described in more detail. The red-band lightcomponent transmitted through the dichroic mirror DM101 is changed inits optical path by 90° by a reflecting mirror M101, passes through afield lens 107R, becomes incident on an incident-side polarizing plate108RI and liquid crystal display element 109R, and is modulated here.

The modulated red-band light component strikes an exit-side polarizingplate 110RO and dichroic prism 111 in this order. The optical path ischanged by 90° by the dichroic prism 111. Then, the light componentbecomes incident on the projecting lens 112. The dichroic prism 111 isformed by bonding four prisms with adhesive such that it has an almostcross-shaped wavelength selection reflecting layer.

On the other hand, the green- and blue-band light components reflectedand changed in their operation paths by 90° by the dichroic mirror DM101become incident on the dichroic mirror DM102. The dichroic mirror DM102has a characteristic for reflecting a green-band light component G.Hence, the green-band light component is reflected and changed in itsoptical path by 90° by the dichroic mirror DM102, transmitted through afield lens 107G, becomes incident on an incident-side polarizing plate108GI and liquid crystal display element 109G, and is modulated here.

The modulated green-band light component strikes an exit-side polarizingplate 110GO and dichroic prism 111 in this order, passes through thedichroic prism 111, and becomes incident on the projecting lens 112.

The blue-band light component transmitted through the dichroic mirrorDM102 passes through a condenser lens 113, relay lens 114, reflectingmirrors M102 and M103, and field lens 107B, becomes incident on anincident-side polarizing plate 108BI and liquid crystal display element109B, and is modulated here.

The modulated blue-band light component strikes an exit-side polarizingplate 110BO and dichroic prism 111 in this order, is changed in itsoptical path by 90° by the dichroic prism 111, and becomes incident onthe projecting lens 112.

The light components in the respective color bands, which are incidenton the projecting lens 112 in the above-described manner, are projectedonto the projection surface and displayed as an enlarged image.

In the above-described conventional projecting image display apparatus,a polarizing plate is normally formed by bonding a film-shaped polarizerb to transparent substrate a, as shown in FIG. 16, such that apredetermined polarizing characteristic can be exhibited. Both theincident-side polarizing plates and the exit-side polarizing plates areformed by bonding predetermined polarizers to transparent substrates,which have identical shapes independently of colors, for the respectivecolor bands.

An incident-side polarizing plate absorbs light having a rotatingpolarization axis and converts the light into heat to align thepolarization direction of light that becomes incident on a liquidcrystal display element. In an exit-side polarizing plate, when thedisplay color is black, the polarization axis of the polarizing plate isperpendicular to the amplitude of light emerging from a liquid crystaldisplay element. Since all light components are absorbed and convertedinto heat, the heat load is very high.

If the aperture ratio of a liquid crystal display element is low, andthe light amount of a lamp to be used is small, transparent substrates,e.g., glass substrates (the heat conductivity is about 1.2 W/(m·K))having identical shapes suffice, as in the prior art.

Recently, 1.3 inches liquid crystal display elements have an apertureratio of 60% even though the number of pixels is about 770,000. Someliquid crystal display elements improve the brightness of a projectedimage by increasing the power consumption of a lamp. Liquid crystaldisplay elements themselves are also becoming compact.

The heat load changes for each color band and also depending on whetherthe polarizing plate is on the incident side or exit side. For example,when color purity of at least one of a plurality of color bands shouldbe changed, the heat load on the incident- or exit-side polarizing plateof a specific color band increases. For this reason, the heat load onsome incident- or exit-side polarizing plates increases, resulting indegradation in performance of the polarizing plate.

To solve the problem of heat load on a polarizing plate, sapphire whoseheat conductivity (42 W/(m·K)) is about 40 times higher than that of atransparent glass substrate is used as a substrate to which a polarizeris bonded, as is proposed in Japanese Patent Application Laid-Open No.11-231277.

However, sapphire is expensive. Use of sapphire is preferably avoided asmuch as possible from the viewpoint of cost. Especially, a 3-plateprojecting image display apparatus as shown in FIG. 15 uses a total ofsix polarizing plates on the incident and exit sides. Since a pluralityof sapphire substrates are normally required, the cost largelyincreases.

In addition, to increase the cooling efficiency by a cooling fan, thepower consumption of the cooling fan increases, or noise becomes large.

SUMMARY OF THE INVENTION

The present invention has been made to solve the above problems, and hasas its object to provide a projector apparatus which can reduce costwhile reliably preventing any degradation in image quality due to heatby effectively transmitting heat of a polarizing plate to a transparentsubstrate in correspondence with the heat load on the polarizer andefficiently radiating the heat by the transparent substrate.

In order to achieve the above object, according to the presentinvention, there is provided a projector apparatus comprising:

a color separation optical system which separates illumination lightinto a plurality of color light components;

a plurality of image forming panels illuminated with the plurality ofcolor light components, respectively;

a color synthesis optical system which synthesizes the light componentsfrom the plurality of image forming panels illuminated;

a projecting optical system which projects light from the colorsynthesis optical system; and

transparent substrates each arranged on at least one of incident andexit surface sides of the plurality of image forming panels, each of thetransparent substrates holding a polarizer,

wherein a thickness of at least one of the plurality of transparentsubstrates is larger than those of the remaining transparent substrates.

In the present invention, the thickness of the at least one transparentsubstrate is preferably not less than 1.2 times larger than those of theremaining transparent substrates.

In order to achieve the above object, according to the presentinvention, there is also provided a projector apparatus comprising:

a color separation optical system which separates illumination lightinto a plurality of color light components;

a plurality of image forming panels illuminated with the plurality ofcolor light components, respectively;

a color synthesis optical system which synthesizes the light componentsfrom the plurality of image forming panels illuminated;

a projecting optical system which projects light from the colorsynthesis optical system; and

transparent substrates each arranged on at least one of incident andexit surface sides of the plurality of image forming panels, each of thetransparent substrates holding a polarizer,

wherein an area ratio of at least one of the plurality of transparentsubstrates to a polarizer held by the at least one transparent substrateis larger than area ratios of the remaining transparent substrates topolarizers held by the remaining transparent substrates.

In the present invention, the area ratio of the at least one transparentsubstrate to the polarizer held by the at least one transparentsubstrate is not less than 1.2 times larger than the area ratios of theremaining transparent substrates to the polarizers held by the remainingtransparent substrates.

According to the present invention, there is also provided a projectorapparatus comprising:

a color separation optical system which separates illumination lightinto a plurality of color light components;

a plurality of image forming panels illuminated with the plurality ofcolor light components, respectively;

a color synthesis optical system which synthesizes the light componentsfrom the plurality of image forming panels illuminated;

a projecting optical system which projects light from the colorsynthesis optical system; and

transparent substrates each arranged on at least one of incident andexit surface sides of the plurality of image forming panels, each of thetransparent substrates holding a polarizer,

wherein an area of at least one of the plurality of transparentsubstrates is larger than those of the remaining transparent substrates.

In the present invention, the area of the at least one transparentsubstrate is not less than 1.2 times larger than those of the remainingtransparent substrates.

According to the present invention, there is also provided a projectorapparatus comprising:

a color separation optical system which separates illumination lightinto a plurality of color light components;

a plurality of image forming panels illuminated with the plurality ofcolor light components, respectively;

a color synthesis optical system which synthesizes the light componentsfrom the plurality of image forming panels illuminated;

a projecting optical system which projects light from the colorsynthesis optical system; and

transparent substrates each arranged on at least one of incident andexit surface sides of the plurality of image forming panels, each of thetransparent substrates holding a polarizer,

wherein a surface area of at least one of the plurality of transparentsubstrates is larger than those of the remaining transparent substrates.

In the present invention, the at least one transparent substrate has ashape with a curvature, and the remaining transparent substrates have aplanar shape.

In the present invention, the plurality of transparent substrates areessentially formed from a material selected from the group consisting ofsapphire, fluorite, and glass.

Additionally, in the present invention, the at least one of theplurality of transparent substrates and the remaining transparentsubstrates are essentially formed from different materials selected fromthe group consisting of sapphire, fluorite, and glass.

Furthermore, in the present invention, the at least one transparentsubstrate of the plurality of transparent substrates is essentiallyformed from a material selected from the group consisting of sapphire,fluorite, and glass, and the remaining transparent substrates areessentially formed from one or two materials which are different fromthe material of the at least one transparent substrate and are selectedfrom the group consisting of sapphire, fluorite, and glass.

The above and other objects, features, and advantages of the presentinvention will become apparent in the embodiments to be described laterin conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view showing the optical arrangement of a projecting imagedisplay apparatus (projector apparatus) according to the firstembodiment of the present invention;

FIG. 2 is a perspective view showing the structure of a red-bandpolarizing plate in the projecting image display apparatus according tothe first embodiment;

FIG. 3 is a graph showing the relationship between the thickness of atransparent substrate and the temperature of the bonding interface of apolarizer in the projecting image display apparatus according to thefirst embodiment;

FIGS. 4A and 4B are views showing combinations of heat load and thematerials and thicknesses of transparent substrates in the projectingimage display apparatus according to the first embodiment of the presentinvention;

FIGS. 5A and 5B are views showing other combinations of heat load andthe materials and thicknesses of transparent substrates in theprojecting image display apparatus according to the first embodiment ofthe present invention;

FIG. 6 is a view showing the optical arrangement of a projecting imagedisplay apparatus (projector apparatus) according to the secondembodiment of the present invention;

FIG. 7 is a perspective view showing the structure of a red-bandpolarizing plate in the projecting image display apparatus according tothe second embodiment;

FIG. 8 is a graph showing the relationship between the area ratio of atransparent substrate to a polarizer and the temperature of the bondinginterface of a polarizer in the projecting image display apparatusaccording to the second embodiment;

FIGS. 9A and 9B are views showing combinations of heat load and thematerials and area ratios of transparent substrates in the projectingimage display apparatus according to the second embodiment of thepresent invention;

FIGS. 10A and 10B are views showing other combinations of heat load andthe materials and area ratios of transparent substrates in theprojecting image display apparatus according to the second embodiment ofthe present invention;

FIG. 11 is a view showing the optical arrangement of a projecting imagedisplay apparatus (projector apparatus) according to the thirdembodiment of the present invention;

FIG. 12 is a perspective view showing the structure of a field lenshaving a red-band polarizer in the projecting image display apparatusaccording to the third embodiment;

FIGS. 13A and 13B are views showing combinations of heat load and thematerials and shapes of transparent substrates in the projecting imagedisplay apparatus according to the third embodiment of the presentinvention;

FIGS. 14A and 14B are views showing other combinations of heat load andthe materials and shapes of transparent substrates in the projectingimage display apparatus according to the third embodiment of the presentinvention;

FIG. 15 is a view showing the optical arrangement of a conventionalprojecting image display apparatus; and

FIG. 16 is a perspective view showing the structure of a polarizingplate in the conventional projecting image display apparatus.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows the optical arrangement of a projecting image displayapparatus (projector apparatus) according to the first embodiment of thepresent invention.

Referring to FIG. 1, white illumination light emitted from a lightsource section 1 of an ultrahigh-pressure mercury-vapor lamp isreflected by a reflector 2 and transmitted through fly-eye lenses 3 and4. The direction of polarization is aligned through a PS conversionelement 5 by a mirror which separates light into p-polarized light ands-polarized light and a λ/2-plate which changes the polarizationdirection. The light that emerges from the PS conversion element 5passes through a condenser lens 6 and the like. After that, a red-bandlight component is transmitted through a dichroic mirror DM1. Green- andblue-band light components are reflected by the dichroic mirror DM1. Theblue-band light component is transmitted through a dichroic mirror DM2.The green-band light component is reflected by the dichroic mirror DM2.With this arrangement, the illumination light is separated into thelight components in the red, green, and blue bands. The dichroic mirrorsform a color separation optical system.

Each color light component becomes incident on a corresponding one ofliquid crystal display elements 9R, 9G, and 9B to form each color image.The color images are synthesized by a dichroic prism 11 serving as acolor synthesis optical system and then projected onto a projectionsurface (screen) (not shown) by a projecting lens 12 serving as aprojecting optical system. Each of the above liquid crystal displayelements is an image forming panel such as a liquid crystal displaypanel. A transmission-type image forming panel for passing light to forman image is used.

Each color band will be described in more detail. The red-band lightcomponent transmitted through the dichroic mirror DM1 is changed in itsoptical path by 90° by a reflecting mirror M1, passes through a fieldlens 7R, and becomes incident on an incident-side polarizing plate 8RIand liquid crystal display element 9R. The liquid crystal displayelement 9R is driven in accordance with image information supplied froman image information supply apparatus (e.g., a personal computer, TV,video tape recorder, or DVD player) (not shown) and modulates thered-band light component incident thereon.

The modulated red-band light component strikes an exit-side polarizingplate 10RO and dichroic prism 11 in this order. The optical path ischanged by 90° by the dichroic prism 11. Then, the light componentbecomes incident on the projecting lens 12. The dichroic prism 11 is aso-called cross dichroic prism formed by bonding four prisms withadhesive such that it has an almost cross-shaped wavelength selectionreflecting (dichroic) layer. In place of the cross dichroic prism, aso-called 3P (3-piece) or a 4P (4-piece) prism formed by bonding threeor four prisms having different shapes may be used. The cross dichroicprism, 3P (3-piece) prism, or 4P (4-piece) prism constructs a colorsynthesis optical system.

On the other hand, the green- and blue-band light components reflectedand changed in their operation paths by 90° by the dichroic mirror DM1become incident on the dichroic mirror DM2. The dichroic mirror DM2 hasa characteristic for reflecting a green-band light component G. Hence,the green-band light component is reflected and changed in its opticalpath by 90° by the dichroic mirror DM2, transmitted through a field lens7G, and becomes incident on an incident-side polarizing plate 8GI andliquid crystal display element 9G. The liquid crystal display element 9Gis driven in accordance with image information supplied from an imageinformation supply apparatus (not shown) and modulates the green-bandlight component incident thereon.

The modulated green-band light component strikes an exit-side polarizingplate 10GO and dichroic prism 11 in this order, passes through thedichroic prism 11, and becomes incident on the projecting lens 12.

The blue-band light component transmitted through the dichroic mirrorDM2 is transmitted through a condenser lens 13, changed in its opticalpath by 90° by a reflecting mirror M2, transmitted through a relay lens14, changed in its optical path by 90° again by a reflecting mirror M3,transmitted through a field lens 7B, and becomes incident on anincident-side polarizing plate 8BI and liquid crystal display element9B. The liquid crystal display element 9B is driven in accordance withimage information supplied from an image information supply apparatus(not shown) and modulates the blue-band light component incidentthereon.

The modulated blue-band light component strikes an exit-side polarizingplate 10BO and dichroic prism 11 in this order, is changed in itsoptical path by 90° by the dichroic prism 11, and becomes incident onthe projecting lens 12.

The light components in the respective color bands, which aresynthesized by the dichroic prism 11, are projected onto the projectionsurface (screen) (not shown) by the projecting lens 12 and displayed asan enlarged image.

When the color purity of the red band is reduced (when another colorband near the red band is also included), a bright image is obtained. Inthis case, however, the heat load on the polarizing plate arranged inthe optical path of the red band increases.

A measure against this will be described below. As shown in FIG. 2, inthe incident-side polarizing plate 8RI (exit-side polarizing plate 10RO)which passes a red-band light component, a polarizer 8 b (10 b) isbonded to (held by) a transparent substrate 8 a (10 a) such that apredetermined polarizing characteristic can be exhibited. If thetransparent substrates corresponding to the red-, green-, and blue-bandlight components are to be made of the same material such as fluorite, athickness t of the transparent substrate which passes the red-band lightcomponent is set to be larger than that of the transparent substrate ofthe incident-side polarizing plate 8GI or exit-side polarizing plate10GO which passes the green-band light component or the incident-sidepolarizing plate 8BI or exit-side polarizing plate 10BO which passes theblue-band light component.

The relationship between the thickness of a transparent substrate andthe temperature of the bonding interface of a polarizer will bedescribed with reference to FIG. 3. FIG. 3 shows the relationshipbetween the thickness of a transparent substrate and the temperature ofthe bonding interface of a polarizer when a polarizer having apredetermined area is bonded to a transparent substrate having apredetermined area, and the polarizer generates predetermined heat. FIG.3 shows the relationship for each of cases wherein the transparentsubstrates are formed from glass (BK7: heat conductivity: about 1.2W/(m·K)), the transparent substrates are formed from fluorite (heatconductivity: about 9.7 W/(m·K)), and the transparent substrates areformed from sapphire (heat conductivity: 42 W/(m·K)).

The result shown in FIG. 3 is obtained when only cooling by naturalconvection of air is executed without forcible cooling.

As is apparent from FIG. 3, if the transparent substrates are made ofthe same material, the maximum temperature becomes lower as the boardthickness of the transparent substrate increases. That is, to preventany degradation in performance due to heat of the polarizer, a largeboard thickness is more advantageous. The result obtained when apolarizer is bonded to a sapphire substrate having a board thickness of0.5 mm is the same as the result obtained when a polarizer is bonded toa fluorite substrate having a board thickness of 1.1 mm.

As is apparent from this fact, even when the transparent substrate 8 a(10 a) of the incident-side polarizing plate 8RI or exit-side polarizingplate 10RO which passes the red-band light component is made offluorite, the heat load can be sufficiently relaxed by making the boardthickness of the transparent substrate larger than those of theremaining transparent substrates. More specifically, when thetransparent substrate which passes the red-band light component isthicker than the transparent substrates which pass the remaining bandlight components by about 20% (about 1.2 times), the difference becomesconspicuous.

In this embodiment, the fluorite transparent substrates used for theincident- and exit-side polarizing plates arranged in the optical pathof the red-band light component are made thicker than the fluoritetransparent substrates used for the incident- and exit-side polarizingplates arranged in the optical paths of the remaining band lightcomponents. However, the transparent substrates of the incident- andexit-side polarizing plates arranged in the optical path of the green-or blue-band light component, for which the heat load increases due tothe cooling air channel or the like, may be made thicker than those forthe remaining band light components.

In addition, of the incident- and exit-side polarizing plates, only thetransparent substrate of a polarizing plate with a high heat load may bethick.

The material of the transparent substrate is not limited to fluorite. Aglass transparent substrate may be used depending on the degree of heatload. In this case as well, when the board thickness is increased byabout 20%, the difference becomes conspicuous, as is apparent from FIG.3.

In the above-described embodiment, the board thickness of a transparentsubstrate is changed in accordance with heat load whereby the heat ofthe polarizing plate can be effectively transmitted to the transparentsubstrate and efficiently radiated by the transparent substrate.

Combinations of heat load and the materials and board thicknesses oftransparent substrates when one of a plurality of transparent substratesis formed from a material different from that of the remainingtransparent substrates will be described with reference to FIGS. 4A and4B and FIGS. 5A and 5B. Two or three kinds of materials are used.

Referring to FIG. 4A, incident- or exit-side polarizing plates a, b, andc are arranged in three optical paths of light components separated intothree colors, respectively. For each polarizing plate, a polarizer isbonded to a transparent substrate.

Assume that the heat load on the respective polarizing plates increasesin an order of a, b, and c (in the polarizing plates a, b, and c, thepolarizing plate a has the highest heat load, and the polarizing plate chas the lowest heat load). The transparent substrate of the polarizingplate a is thicker (e.g., thicker by 1.2 times or more) than those ofthe polarizing plates b and c.

FIG. 4B shows effective combinations when two or more kinds of materialsare used for transparent substrates with the above arrangement. FIG. 4Bshows a table of combinations when materials A and B (heat conductivity:A>B) are employed for the transparent substrates of the polarizingplates a, b, and c shown in FIG. 4A. As one case, sapphire is used asthe material A, and fluorite (and/or glass) is used as the material B.As another case, sapphire (and/or fluorite) is used as the material A,and glass is used as the material B. There are choices of combinations 1to 4. An optimum combination is selected in accordance with thesituation of heat load or the degree of freedom in design. For example,in combination 2, the transparent substrate used for the polarizingplate a is made of sapphire, i.e., the material A, and the transparentsubstrates used for the polarizing plates b and c are made of fluorite(or glass), i.e., the material B. Alternatively, the transparentsubstrate used for the polarizing plate a is made of sapphire, i.e., thematerial A, the transparent substrate used for the polarizing plate b ismade of fluorite, i.e., the material B, and the transparent substrateused for the polarizing plate c is made of glass, i.e., the material B.

If the heat load on a given polarizing plate is very high, a sapphiresubstrate is used only for the transparent substrate of that polarizingplate, and the board thickness of the transparent substrate isincreased. With this arrangement, the polarizing plate can reliablystand the high heat load.

Combinations when transparent substrates are thick in two optical pathswill be described next.

Referring to FIG. 5A, incident- or exit-side polarizing plates d, e, andf are arranged in three optical paths of light components separated intothree colors, respectively. For each polarizing plate, a polarizer isbonded to a transparent substrate.

Assume that the heat load on the respective polarizing plates increasesin an order of d, e, and f (in the polarizing plates d, e and f, thepolarizing plate d has the highest heat load, and the polarizing plate fhas the lowest heat load). The transparent substrates of the polarizingplates d and e are thicker (e.g., thicker by 1.2 times or more) thanthat of the polarizing plate f.

FIG. 5B shows effective combinations when two or more kinds of materialsare used for transparent substrates with the above arrangement. FIG. 5Bshows a table of combinations when materials C and D (heat conductivity:C>D) are employed for the transparent substrates of the polarizingplates d, e, and f shown in FIG. 5A. As one case, sapphire is used asthe material C, and fluorite (and/or glass) is used as the material D.As another case, sapphire (and/or fluorite) is used as the material C,and glass is used as the material D. There are choices of combinations 5to 8. An optimum combination is selected in accordance with thesituation of heat load or the degree of freedom in design. For example,in combination 6, the transparent substrate used for the polarizingplate d is made of sapphire, i.e., the material C, and the transparentsubstrates used for the polarizing plates e and f are made of fluorite,i.e., the material D. Alternatively, the transparent substrate used forthe polarizing plate d is made of sapphire, i.e., the material C, thetransparent substrate used for the polarizing plate e is made offluorite (or glass), i.e., the material D, and the transparent substrateused for the polarizing plate f is made of glass (or fluorite), i.e.,the material D.

In the above-described embodiment, the material of a transparentsubstrate is selected, and the board thickness of the transparentsubstrate is changed in accordance with heat load whereby the heat ofthe polarizing plate can be effectively transmitted to the transparentsubstrate and efficiently radiated by the transparent substrate.

FIG. 6 shows the optical arrangement of a projecting image displayapparatus (projector apparatus) according to the second embodiment ofthe present invention. The same reference numerals as in the firstembodiment denote the same components in the second embodiment.

Referring to FIG. 6, white light emitted from a light source section 1of an ultrahigh-pressure mercury-vapor lamp is reflected by a reflector2 and transmitted through fly-eye lenses 3 and 4. The direction ofpolarization is aligned through a PS conversion element 5 by a mirrorwhich separates light into p-polarized light and s-polarized light and aλ/2-plate which changes the polarization direction. The light thatemerges from the PS conversion element 5 passes through a condenser lens6 and the like. After that, a dichroic mirror DM1 passes a red-bandlight component and reflects green- and blue-band light components. Theblue-band light component is transmitted through a dichroic mirror DM2.The green-band light component is reflected by the dichroic mirror DM2.With this arrangement, the illumination light is separated into thelight components in the red, green, and blue bands. The dichroic mirrorsform a color separation optical system.

Each color light component becomes incident on a corresponding one ofliquid crystal display elements 9R, 9G, and 9B and is modulated. Thecolor light components are synthesized by a dichroic prism 11 serving asa color synthesis optical system and then projected onto a projectionsurface (screen) (not shown) by a projecting lens 12 serving as aprojecting optical system. Each of the above liquid crystal displayelements is an image forming panel such as a liquid crystal displaypanel. A transmission-type image forming panel for passing light to forman image is used.

Each color band will be described in more detail. The red-band lightcomponent transmitted through the dichroic mirror DM1 is changed in itsoptical path by 90° by a reflecting mirror M1, passes through a fieldlens 7R, and becomes incident on an incident-side polarizing plate 18RIand liquid crystal display element 9R. The liquid crystal displayelement 9R is driven in accordance with image information supplied froman image information supply apparatus (e.g., a personal computer, TV,video tape recorder, or DVD player) (not shown) and modulates thered-band light component incident thereon.

The modulated red-band light component strikes an exit-side polarizingplate 20RO and dichroic prism 11 in this order. The optical path ischanged by 90° by the dichroic prism 11. Then, the light componentbecomes incident on the projecting lens 12. The dichroic prism 11 is aso-called cross dichroic prism formed by bonding four prisms withadhesive such that it has an almost cross-shaped wavelength selectionreflecting (dichroic) layer. In place of the cross dichroic prism, aso-called 3P (3-piece) or a 4P (4-piece) prism formed by bonding threeor four prisms having different shapes may be used. The cross dichroicprism, 3P (3-piece) prism, or 4P (4-piece) prism constructs a colorsynthesis optical system.

On the other hand, the green- and blue-band light components reflectedand changed in their operation paths by 90° by the dichroic mirror DM1become incident on the dichroic mirror DM2. The dichroic mirror DM2 hasa characteristic for reflecting a green-band light component G. Hence,the green-band light component is reflected and changed in its opticalpath by 90° by the dichroic mirror DM2, transmitted through a field lens7G, and becomes incident on an incident-side polarizing plate 8GI andliquid crystal display element 9G. The liquid crystal display element 9Gis driven in accordance with image information supplied from an imageinformation supply apparatus (not shown) and modulates the green-bandlight component incident thereon.

The modulated green-band light component strikes an exit-side polarizingplate 10GO and dichroic prism 11 in this order, passes through thedichroic prism 11, and becomes incident on the projecting lens 12.

The blue-band light component transmitted through the dichroic mirrorDM2 is transmitted through a condenser lens 13, changed in its opticalpath by 90° by a reflecting mirror M2, transmitted through a relay lens14, changed in its optical path by 90° again by a reflecting mirror M3,transmitted through a field lens 7B, and becomes incident on anincident-side polarizing plate 8BI and liquid crystal display element9B. The liquid crystal display element 9B is driven in accordance withimage information supplied from an image information supply apparatus(not shown) and modulates the blue-band light component incidentthereon.

The modulated blue-band light component strikes an exit-side polarizingplate 10BO and dichroic prism 11 in this order, is changed in itsoptical path by 90° by the dichroic prism 11, and becomes incident onthe projecting lens 12.

The light components in the respective color bands, which aresynthesized by the dichroic prism 11, are projected onto the projectionsurface (screen) (not shown) by the projecting lens 12 and displayed asan enlarged image.

When the color purity of the red band is reduced (when another colorband light near the red band is also included), a bright image isobtained. In this case, however, the heat load on the polarizing platearranged in the optical path of the red band increases.

A measure against this will be described below. As shown in FIG. 7, inthe incident-side polarizing plate 18RI (exit-side polarizing plate20RO) which passes a red-band light component, a polarizer 18 b (20 b)is bonded to a transparent substrate 18 a (20 a) such that apredetermined polarizing characteristic can be exhibited.

If the transparent substrates corresponding to the red-, green-, andblue-band light components are to be made of the same material such asfluorite, the area of a surface of the transparent substrate 18 a (20 a)which passes the red-band light component, to which the polarizer 18 b(20 b) is to be bonded, is set to be larger than that of a surface, towhich a polarizer is to be bonded, of the transparent substrate of theincident-side polarizing plate 8GI or exit-side polarizing plate 10GOwhich passes the green-band light component or the incident-sidepolarizing plate 8BI or exit-side polarizing plate 10BO which passes theblue-band light component.

The relationship between the area ratio of a transparent substrate to apolarizer and the temperature of the surface of the transparentsubstrate, to which the polarizer is bonded will be described withreference to FIG. 8. FIG. 8 shows the relationship between the arearatio of a transparent substrate to a polarizer (when a polarizer has apredetermined area, the bonding area of the polarizer) and thetemperature of the surface of the transparent substrate, to which thepolarizer is bonded when a polarizer having a predetermined area isbonded to each of transparent substrates having thicknesses of 1 mm, 2mm, and 3 mm, and the polarizer generates predetermined heat. Thematerial of a transparent substrate is fluorite.

The result shown in FIG. 8 is obtained when only cooling by naturalconvection of air is executed without forcible cooling.

As is apparent from FIG. 8, if the transparent substrates have the samethickness, the maximum temperature of the bonding interface becomeslower as the ratio of the area of the bonding interface of thetransparent substrate to the area of the polarizer (transparentsubstrate area/polarizer area) increases. That is, to prevent anydegradation in performance due to heat of the polarizer, a high arearatio is more advantageous. The result obtained when a polarizer isbonded to a fluorite substrate having a thickness of 1 mm and an arearatio of 2.0 is the same as the result obtained when a polarizer isbonded to a fluorite substrate having a thickness of 3 mm and an arearatio of 1.2. Even when the material of a transparent substrate issapphire or glass, the same characteristic as in fluorite can beexhibited.

As is apparent from this fact, even when the transparent substrate 18 a(20 a) of the incident-side polarizing plate 18RI or exit-sidepolarizing plate 20RO which passes the red-band light component is madeof fluorite, the heat load can be sufficiently relaxed by increasing thearea ratio. More specifically, when the area ratio is higher than thearea ratios of the transparent substrates which pass the remaining bandlight components to the polarizers by about 20% (about 1.2 times), thedifference becomes conspicuous.

In this embodiment, the area ratio of the fluorite transparentsubstrates used for the incident- and exit-side polarizing platesarranged in the optical path of the red-band light component to thepolarizers bonded to the transparent substrates is made higher than thearea ratio of the fluorite transparent substrates used for the incident-and exit-side polarizing plates arranged in the optical paths of theremaining band light components to the polarizers bonded to thetransparent substrates. However, the area ratio of the transparentsubstrates of the incident- and exit-side polarizing plates arranged inthe optical path of the green- or blue-band light component, for whichthe heat load increases due to the cooling air channel or the like, maybe made higher than those for the remaining band light components.

In addition, of the incident- and exit-side polarizing plates, only thearea ratio of the transparent substrate of a polarizing plate with ahigh heat load to a polarizer bonded to the transparent substrate may behigh.

The material of the transparent substrate is not limited to fluorite. Aglass (or sapphire) transparent substrate may be used depending on thedegree of heat load. In this case as well, when the area ratio isincreased by about 20%, the difference becomes conspicuous.

In the above-described embodiment, the area of a transparent substrateis changed in accordance with heat load whereby the heat of thepolarizing plate can be effectively transmitted to the transparentsubstrate and efficiently radiated by the transparent substrate.

Combinations of heat load and the materials and area ratios oftransparent substrates when one of a plurality of transparent substratesis formed from a material different from that of the remainingtransparent substrates will be described with reference to FIGS. 9A and9B and FIGS. 10A and 10B. Two or three kinds of materials are used.

Referring to FIG. 9A, incident- or exit-side polarizing plates a, b, andc are arranged in three optical paths of light components separated intothree colors, respectively. For each polarizing plate, a polarizer isbonded to a transparent substrate.

Assume that the heat load on the respective polarizing plates increasesin an order of a, b, and c (in the polarizing plates a, b, and c, thepolarizing plate a has the highest heat load, and the polarizing plate chas the lowest heat load). The area of the transparent substrate of thepolarizing plate a is larger (e.g., larger by 1.2 times or more) thanthe areas of the transparent substrates of the polarizing plates b andc.

FIG. 9B shows effective combinations when two or more kinds of materialsare used for transparent substrates with the above arrangement. FIG. 9Bshows a table of combinations when materials A and B (heat conductivity:A>B) are employed for the transparent substrates of the polarizingplates a, b, and c shown in FIG. 9A. As one case, sapphire is used asthe material A, and fluorite (and/or glass) is used as the material B.As another case, sapphire (and/or fluorite) is used as the material A,and glass is used as the material B. There are choices of combinations 1to 4. An optimum combination is selected in accordance with thesituation of heat load or the degree of freedom in design. For example,in combination 2, the transparent substrate used for the polarizingplate a is made of sapphire, i.e., the material A, and the transparentsubstrates used for the polarizing plates b and c are made of fluorite(or glass), i.e., the material B. Alternatively, the transparentsubstrate used for the polarizing plate a is made of sapphire, i.e., thematerial A, the transparent substrate used for the polarizing plate b ismade of fluorite, i.e., the material B, and the transparent substrateused for the polarizing plate c is made of glass, i.e., the material B.

As described above, if the heat load on a given polarizing plate is veryhigh, a sapphire substrate is used only for the transparent substrate ofthat polarizing plate, and the area ratio is increased. With thisarrangement, the polarizing plate can reliably stand the high heat load.

Combinations when the area ratios of transparent substrates topolarizers are high in two optical paths will be described next.

Referring to FIG. 10A, incident- or exit-side polarizing plates d, e,and f are arranged in three optical paths of light components separatedinto three colors, respectively. For each polarizing plate, a polarizeris bonded to a transparent substrate.

Assume that the heat load on the respective polarizing plates increasesin an order of d, e, and f (in the polarizing plates d, e and f, thepolarizing plate d has the highest heat load, and the polarizing plate fhas the lowest heat load). The area of the transparent substrates of thepolarizing plates d and e is larger (e.g., larger by 1.2 times or more)than the area of the transparent substrate of the polarizing plate f.

FIG. 10B shows effective combinations when two or more kinds ofmaterials are used for transparent substrates with the abovearrangement. FIG. 10B shows a table of combinations when materials C andD (heat conductivity: C>D) are employed for the transparent substratesof the polarizing plates d, e, and f shown in FIG. 10A. As one case,sapphire is used as the material C, and fluorite (and/or glass) is usedas the material D. As another case, sapphire (and/or fluorite) is usedas the material C, and glass is used as the material D. There arechoices of combinations 5 to 8. An optimum combination is selected inaccordance with the situation of heat load or the degree of freedom indesign. For example, in combination 6, the transparent substrate usedfor the polarizing plate d is made of sapphire, i.e., the material C,and the transparent substrates used for the polarizing plates e and fare made of fluorite (or glass), i.e., the material D. Alternatively,the transparent substrate used for the polarizing plate d is made ofsapphire, i.e., the material C, the transparent substrate used for thepolarizing plate e is made of fluorite (or glass), i.e., the material D,and the transparent substrate used for the polarizing plate f is made ofglass (or fluorite), i.e., the material D.

In the above-described embodiment, the material of a transparentsubstrate is selected, and the area of the transparent substrate ischanged in accordance with heat load whereby the heat of the polarizingplate can be effectively transmitted to the transparent substrate andefficiently radiated by the transparent substrate.

FIG. 11 shows the optical arrangement of a projecting image displayapparatus (projector apparatus) according to the third embodiment of thepresent invention. The same reference numerals as in the firstembodiment denote the same components in the third embodiment.

Referring to FIG. 11, white light emitted from a light source section 1of an ultrahigh-pressure mercury-vapor lamp is reflected by a reflector2 and transmitted through fly-eye lenses 3 and 4. The direction ofpolarization is aligned through a PS conversion element 5 by a mirrorwhich separates light into p-polarized light and s-polarized light and aλ/2-plate which changes the polarization direction. The light thatemerges from the PS conversion element 5 passes through a condenser lens6 and the like. After that, a dichroic mirror DM1 passes a red-bandlight component and reflects green- and blue-band light components. Theblue-band light component is transmitted through a dichroic mirror DM2.The green-band light component is reflected by the dichroic mirror DM2.With this arrangement, the illumination light is separated into thelight components in the red, green, and blue bands. The dichroic mirrorsform a color separation optical system.

Each color light component becomes incident on a corresponding one ofliquid crystal display elements 9R, 9G, and 9B and is modulated. Thecolor light components are synthesized by a dichroic prism 11 serving asa color synthesis optical system and then projected onto a projectionsurface (screen) (not shown) by a projecting lens 12 serving as aprojecting optical system. Each of the above liquid crystal displayelements is an image forming panel such as a liquid crystal displaypanel. A transmission-type image forming panel for passing light to forman image is used.

Each color band will be described in more detail. The red-band lightcomponent transmitted through the dichroic mirror DM1 is changed in itsoptical path by 90° by a reflecting mirror M1, passes through a fieldlens 28RI with polarizer, and becomes incident on the liquid crystaldisplay element 9R. The liquid crystal display element 9R is driven inaccordance with image information supplied from an image informationsupply apparatus (e.g., a personal computer, TV, video tape recorder, orDVD player) (not shown) and modulates the red-band light componentincident thereon.

The modulated red-band light component strikes an exit-side polarizingplate 10RO and dichroic prism 11 in this order. The optical path ischanged by 90° by the dichroic prism 11. Then, the light componentbecomes incident on the projecting lens 12. The dichroic prism 11 is aso-called cross dichroic prism formed by bonding four prisms withadhesive such that it has an almost cross-shaped wavelength selectionreflecting (dichroic) layer. In place of the cross dichroic prism, aso-called 3P (3-piece) or a 4P (4-piece) prism formed by bonding threeor four prisms having different shapes may be used. The cross dichroicprism, 3P (3-piece) prism, or 4P (4-piece) prism constructs a colorsynthesis optical system.

On the other hand, the green- and blue-band light components reflectedand changed in their operation paths by 90° by the dichroic mirror DM1become incident on the dichroic mirror DM2. The dichroic mirror DM2 hasa characteristic for reflecting a green-band light component G. Hence,the green-band light component is reflected and changed in its opticalpath by 90° by the dichroic mirror DM2, transmitted through a field lens7G, and becomes incident on an incident-side polarizing plate 8GI andliquid crystal display element 9G. The liquid crystal display element 9Gis driven in accordance with image information supplied from an imageinformation supply apparatus (not shown) and modulates the green-bandlight component incident thereon.

The modulated green-band light component strikes an exit-side polarizingplate 10GO and dichroic prism 11 in this order, passes through thedichroic prism 11, and becomes incident on the projecting lens 12.

The blue-band light component transmitted through the dichroic mirrorDM2 is transmitted through a condenser lens 13, relay lens 14,reflecting mirrors M2 and M3, and field lens 7B and becomes incident onan incident-side polarizing plate 8BI and liquid crystal display element9B. The liquid crystal display element 9B is driven in accordance withimage information supplied from an image information supply apparatus(not shown) and modulates the blue-band light component incidentthereon.

The modulated blue-band light component strikes an exit-side polarizingplate 10BO and dichroic prism 11 in this order, is changed in itsoptical path by 90° by the dichroic prism 11, and becomes incident onthe projecting lens 12.

The light components in the respective color bands, which aresynthesized by the dichroic prism 11, are projected onto the projectionsurface (screen) (not shown) by the projecting lens 12 and displayed asan enlarged image.

When the color purity of the red band is reduced (when another colorband light near the red band is also included), a bright image isobtained. In this case, however, the heat load on the polarizing platearranged in the optical path of the red band increases.

A measure against this will be described below. As shown in FIG. 12, thefield lens 28RI used as the transparent substrate of the polarizingplate which passes a red-band light component is formed by bonding apolarizer 28 b to the exit plane of a lens section (corresponding to atransparent substrate) 28 a such that a predetermined polarizingcharacteristic can be exhibited. The field lens and transparentsubstrate are formed from the same material, i.e., fluorite.

The field lens serving as one transparent substrate has a shapedifferent from the planar shape of each of the remaining transparentsubstrates. The incident surface of the lens section 28 a of the fieldlens is formed from a spherical surface (alternatively, a convexsurface, concave surface, aspherical surface, or free-form surface maybe possible). Its size or thickness at the center can be relativelyfreely set. That is, the surface area of one transparent substrate islarger than those of the remaining transparent substrates. In thisembodiment, the shape (the area or thickness of the lens 28 a) of thefield lens serving as one transparent substrate is set to be different(larger in area or thickness) from the planar shape of the transparentsubstrate of the incident-side polarizing plate 8GI or exit-sidepolarizing plate 10GO which passes the green-band light component or theincident-side polarizing plate 8BI or exit-side polarizing plate 10BOwhich passes the blue-band light component. That is, the field lensserving as one transparent substrate has a shape different from those ofthe remaining transparent substrates (the surface area of onetransparent substrate (field lens) is larger than those of the remainingtransparent substrates).

In this embodiment as well, when the shape of the transparent substrate(field lens 28RI) to which an incident-side polarizer which passes thered-band light component is bonded is appropriately optimized on thebasis of the relationship shown in FIG. 3 of the first embodiment orFIG. 8 of the second embodiment, the heat load can be sufficientlyrelaxed even when fluorite is used as the material of the transparentsubstrate (lens).

In this embodiment, an incident-side polarizer is bonded to the fieldlens serving as a transparent substrate arranged in the optical path ofthe red-band light component, and the shape of the field lens isoptimized. However, the transparent substrate of the green or blue band,for which the heat load increases due to the cooling air channel or thelike, may serve as a field lens, and a polarizer may be bonded to thefield lens.

Additionally, in this embodiment, a polarizer is bonded to a field lensmade of fluorite, and the shape of the field lens is optimized.Depending on the degree of heat load, a polarizer may be boned to aglass field lens, and the shape of the field lens may be optimized.

In the above embodiment, as the shape of the transparent substrate, thefield lens has a planar surface on one side and a spherical lens sectionon the other side. However, if the surface area becomes larger than thatof a planar transparent substrate, and the display image to be projectedis not affected, the polarizer may be held by a planar surface on oneside, and the surface on the other side may be formed into a wave shapeor grating shape such that the surface area becomes larger than a planarsurface.

Combinations of heat load and the materials and shapes of transparentsubstrates when one of a plurality of transparent substrates is formedfrom a material different from that of the remaining transparentsubstrates will be described with reference to FIGS. 13A and 13B andFIGS. 14A and 14B. Two or three kinds of materials are used.

Referring to FIG. 13A, incident- or exit-side polarizing plates a, b,and c are arranged in three optical paths of light components separatedinto three colors, respectively. For each polarizing plate, a polarizeris bonded to a transparent substrate.

Assume that the heat load on the respective polarizing plates increasesin an order of a, b, and c (in the polarizing plates a, b, and c, thepolarizing plate a has the highest heat load, and the polarizing plate chas the lowest heat load). The transparent substrate of the polarizingplate a has a shape different from the planar shapes of the polarizingplates b and c and has a larger surface area and volume (a field lens inwhich one surface has a planar shape and the other surface has aspherical shape is used).

FIG. 13B shows effective combinations when two or more kinds ofmaterials are used for transparent substrates with the abovearrangement. FIG. 13B shows a table of combinations when materials A andB (heat conductivity: A>B) are employed for the transparent substratesof the polarizing plates a, b, and c shown in FIG. 13A. As one case,sapphire is used as the material A, and fluorite (and/or glass) is usedas the material B. As another case, sapphire (and/or fluorite) is usedas the material A, and glass is used as the material B. There arechoices of combinations 1 to 4. An optimum combination is selected inaccordance with the situation of heat load or the degree of freedom indesign. For example, in combination 2, the transparent substrate usedfor the polarizing plate a is made of sapphire, i.e., the material A,and the transparent substrates used for the polarizing plates b and care made of fluorite (or glass), i.e., the material B. Alternatively,the transparent substrate used for the polarizing plate a is made ofsapphire, i.e., the material A, the transparent substrate used for thepolarizing plate b is made of fluorite, i.e., the material B, and thetransparent substrate used for the polarizing plate c is made of glass,i.e., the material B.

As described above, if the heat load on a given polarizing plate is veryhigh, sapphire is used only for that field lens, and the shape isoptimized (the surface area is increased). With this arrangement, thefield lens (the transparent substrate of the polarizing plate) canreliably stand the high heat load.

Combinations when the shapes of transparent substrates in two opticalpaths are different from that in the remaining optical path will bedescribed next.

Referring to FIG. 14A, incident- or exit-side polarizing plates d, e,and f are arranged in three optical paths of light components separatedinto three colors, respectively. For each polarizing plate, a polarizeris bonded to a transparent substrate.

Assume that the heat load on the respective polarizing plates increasesin an order of d, e, and f (in the polarizing plates d, e and f, thepolarizing plate d has the highest heat load, and the polarizing plate fhas the lowest heat load). The transparent substrates of the polarizingplates d and e have a shape different from the planar shape of thepolarizing plate f and has a larger surface area and volume (fieldlenses in each of which one surface has a planar shape and the othersurface has a spherical shape are used).

FIG. 14B shows effective combinations when two or more kinds ofmaterials are used for transparent substrates with the abovearrangement. FIG. 14B shows a table of combinations when materials C andD (heat conductivity: C>D) are employed for the transparent substratesof the polarizing plates d, e, and f shown in FIG. 14A. As one case,sapphire is used as the material C, and fluorite (and/or glass) is usedas the material D. As another case, sapphire (and/or fluorite) is usedas the material C, and glass is used as the material D. There arechoices of combinations 5 to 8. An optimum combination is selected inaccordance with the situation of heat load or the degree of freedom indesign. For example, in combination 6, the transparent substrate usedfor the polarizing plate d is made of sapphire (or fluorite), i.e., thematerial C, and the transparent substrates used for the polarizingplates e and f are made of fluorite (or glass), i.e., the material D.Alternatively, the transparent substrate used for the polarizing plate dis made of sapphire, i.e., the material C, the transparent substrateused for the polarizing plate e is made of fluorite (or glass), i.e.,the material D, and the transparent substrate used for the polarizingplate f is made of glass (or fluorite), i.e., the material D.

In the above-described embodiment, the material of a transparentsubstrate is selected, and the shape (surface area) of the transparentsubstrate is changed in accordance with heat load whereby the heat ofthe polarizing plate can be effectively transmitted to the transparentsubstrate and efficiently radiated by the transparent substrate.

In the above-described embodiments, in a projector apparatus in which atransmission-type image forming panel such as a liquid crystal displaypanel for passing light to form an image is used as an image formingpanel, a transparent substrate that holds a polarizer in theabove-described embodiments is used. However, a transparent substratethat holds a polarizer in the above-described embodiments may be used ina projector apparatus in which a reflection-type image forming panelsuch as a liquid crystal display panel for reflecting light to form animage is used. In this case, the optical system uses a color separationoptical system, color synthesis optical system, and a colorseparation/synthesis optical system having both functions of colorseparation and color synthesis.

As has been described above, according to each of the above-describedembodiments, the material of a transparent substrate is selected, andthe surface area (thickness, area, or volume) of the transparentsubstrate is changed in accordance with heat load whereby the heat ofthe polarizing plate can be effectively transmitted to the transparentsubstrate and efficiently radiated by the transparent substrate. Theheat load on the polarizing plate can be effectively and sufficientlyrelaxed. Hence, the cost can be reduced while properly preventing anydegradation in image quality due to heat.

1. A projector comprising: a color separation optical system which separates an illumination light into a first color light, a second color light and a third color light; a first image forming panel illuminated with said first color light; a second image forming panel illuminated with said second color light; a third image forming panel illuminated with said third color light; a color synthesis optical system which synthesizes said first color light from said first image forming panel, said second color light from said second image forming panel, and said third color light from said third image forming panel; a projection optical system which projects said synthesized light from said color synthesis optical system; a first polarizing plate disposed between said color separation optical system and said first image forming panel; a second polarizing plate disposed between said color separation optical system and said second image forming panel; and a third polarizing plate disposed between said color separation optical system and said third image forming panel; wherein each of a thickness of said second polarizing plate and a thickness of said third polarizing plate is greater than a thickness of said first polarizing plate.
 2. A projector according to claim 1, wherein said first polarizing plate comprises a first substrate having a polarizer at a first image forming panel side, said second polarizing plate comprises a second substrate having a polarizer at a second image forming panel side, and said third polarizing plate comprises a third substrate having a polarizer at a third image forming panel side.
 3. A projector comprising: a color separation optical system which separates an illumination light into a first color light, a second color light and a third color light; a first image forming panel illuminated with said first color light; a second image forming panel illuminated with said second color light; a third image forming panel illuminated with said third color light; a color synthesis optical system which synthesizes said first color light from said first image forming panel, said second color light from said second image forming panel, and said third color light from said third image forming panel; a projection optical system which projects said synthesized light from said color synthesis optical system; a first polarizing plate disposed between said color separation optical system and said first image forming panel; a second polarizing plate disposed between said color separation optical system and said second image forming panel; and a third polarizing plate disposed between said color separation optical system and said third image forming panel; wherein each of a thermal conductivity of a material of said second polarizing plate and a thermal conductivity of a material of said third polarizing plate is greater than a thermal conductivity of a material of said first polarizing plate.
 4. A projector according to claim 3, wherein said first polarizing plate comprises a first substrate having a polarizer at a first image forming panel side, said second polarizing plate comprises a second substrate having a polarizer at a second image forming panel side, and said third polarizing plate comprises a third substrate having a polarizer at a third image forming panel side.
 5. A projector comprising: a color separation optical system which separates an illumination light into a first color light, a second color light and a third color light; a first image forming panel illuminated with said first color light; a second image forming panel illuminated with said second color light; a third image forming panel illuminated with said third color light; a color synthesis optical system which synthesizes said first color light from said first image forming panel, said second color light from said second image forming panel, and said third color light from said third image forming panel; a projection optical system which projects said synthesized light from said color synthesis optical system; a first substrate disposed between said first image forming panel and said color synthesis optical system; a second substrate disposed between said second image forming panel and said color synthesis optical system; and a third substrate disposed between said third image forming panel and said color synthesis optical system; wherein each of a thickness of said second substrate and a thickness of said third substrate is greater than a thickness of said first substrate.
 6. A projector according to claim 5, wherein said first substrate has a polarizer at a first image forming panel side, said second substrate has a polarizer at a second image forming panel side, and said third substrate has a polarizer at a third image forming panel side.
 7. A projector comprising: a color separation optical system which separates an illumination light into a first color light, a second color light and a third color light; a first image forming panel illuminated with said first color light; a second image forming panel illuminated with said second color light; a third image forming panel illuminated with said third color light; a color synthesis optical system which synthesizes said first color light from said first image forming panel, said second color light from said second image forming panel, and said third color light from said third image forming panel; a projection optical system which projects said synthesized light from said color synthesis optical system; a first substrate disposed between said first image forming panel and said color synthesis optical system; a second substrate disposed between said second image forming panel and said color synthesis optical system; and a third substrate disposed between said third image forming panel and said color synthesis optical system; wherein each of a thermal conductivity of a material of said second substrate and a thermal conductivity of a material of said third substrate is greater than a thermal conductivity of a material of said first substrate.
 8. A projector according to claim 7, wherein said first substrate has a polarizer at a first image forming panel side, said second substrate has a polarizer at a second image forming panel side, and said third substrate has a polarizer at a third image forming panel side.
 9. A projector apparatus comprising: a color separation optical system which separates illumination light into red-band light, blue-band light and green-band light components; a first image forming panel illuminated with said red-band light component; a second image forming panel illuminated with said blue-band light component; a third image forming panel illuminated with said green-band light component; a color synthesis optical system which synthesizes the light components from said first image forming panel, said second image forming panel and said third image forming panel illuminated; a projecting optical system which projects light from said color synthesis optical system; and optical elements for adjustment of polarization condition each arranged on incident and exit surface sides of said first image forming panel, said second image forming panel and said third image forming panel, each of said optical elements including a substrate, wherein each of a thickness of said substrate of said optical element arranged on exit surface side of said second image forming panel and a thickness of said substrate of said optical element arranged on exit surface side of said third image forming panel is greater than a thickness of said substrate of said optical element arranged on exit surface side of said first image forming panel in said optical elements each arranged on exit surface side of said first image forming panel, said second image forming panel and said third image forming panel.
 10. An apparatus according to claim 9, wherein said optical elements include said substrates and polarizers.
 11. A projector apparatus comprising: a color separation optical system which separates illumination light into red-band light, blue-band light and green-band light components; a first image forming panel illuminated with said red-band light component; a second image forming panel illuminated with said blue-band light component; a third image forming panel illuminated with said green-band light component; a color synthesis optical system which synthesizes the light components from said first image forming panel, said second image forming panel and said third image forming panel illuminated; a projecting optical system which projects light from said color synthesis optical system; and optical elements for adjustment of polarization condition each arranged on incident and exit surface sides of said first image forming panel, said second image forming panel and said third image forming panel, each of said optical elements including a substrate, wherein each of an area of said substrate of said optical element arranged on exit surface side of said second image forming panel and an area of said substrate of said optical element arranged on exit surface side of said third image forming panel is greater than an area of said substrate of said optical element arranged on exit surface side of said first image forming panel in said optical elements each arranged on exit surface side of said first image forming panel, said second image forming panel and said third image forming panel.
 12. An apparatus according to claim 11, wherein said optical elements include said substrates and polarizers.
 13. A projector apparatus comprising: a color separation optical system which separates illumination light into red-band light, blue-band light and green-band light components; a first image forming panel illuminated with said red-band light component; a second image forming panel illuminated with said blue-band light component; a third image forming panel illuminated with said green-band light component; a color synthesis optical system which synthesizes the light components from said first image forming panel, said second image forming panel and said third image forming panel illuminated; a projecting optical system which projects light from said color synthesis optical system; and optical elements for adjustment of polarization condition each arranged on incident and exit surface sides of said first image forming panel, said second image forming panel and said third image forming panel, each of said optical elements including a substrate, wherein each of a surface area of said substrate of said optical element arranged on exit surface side of said second image forming panel and a surface area of said substrate of said optical element arranged on exit surface side of said third image forming panel is greater than a surface area of said substrate of said optical element arranged on exit surface side of said first image forming panel in said optical elements each arranged on exit surface side of said first image forming panel, said second image forming panel and said third image forming panel.
 14. An apparatus according to claim 13, wherein said optical elements include said substrates and polarizers. 